The present invention relates to indicators for monitoring the linear extension position of an actuator and, more particularly, to indicators for use in connection with robotic mechanisms.
A linear actuator such as a pneumatic or hydraulic cylinder converts air or hydraulic pressure into a linear force. Linear actuators have a wide variety of applications, one of which is in the field of robotics.
In a robotic application, linear actuators are typically utilized to move robotic mechanisms having multiple axes of motion. For instance, in a paint spray robot, six or more axes of freedom are manipulated in preprogrammed sequences to control, as the desired output, motion of a robot arm which sprays a coating of paint over a surface.
The actuating ends of the linear actuators are connected through linkages to various arms and levers, each of which is typically pivotal about a predetermined axis. It is desirable to monitor the precise position of the actuating end of each linear actuator in order to control the operation of the linkages, arms and levers and to coordinate the operation of each linear actuator with all other linear actuators.
The position of an actuating end of a linear actuator is typically measured by a shaft encoder or a rotating shaft resolver which provides a digital output as a function of the resolver shaft angular rotation position. The digitized quantity, which is purportedly representative of the position of the actuating end of a linear actuator, is delivered to a digital computer processor.
A problem with rotating shaft resolvers is that the position of the actuating or linearly movable end of the piston rod of an actuator is indirectly measured. A robotic mechanism includes a number of rotating gears which function in response to, but at a distance from, linear movement of a particular linear actuator. A rotating shaft resolver is typically connected to such a remote rotating gear and hence measures linear actuation in a circuitous and imprecise fashion.